To date the effective and efficient oral delivery of antisense therapeutics has remained an elusive goal (Tillman 2008). Indeed, oral delivery of oligonucleotide therapeutics has been the subject of considerable research, but despite the concerted efforts, sufficient bioavailability of intact and functional oligonucleotide and the resulting therapeutic benefit has not yet been validated. Modification of oligonucleotide chemistry has created molecules stable enough to survive the intestinal environment; however, efficient absorption has been limited by molecular permeability (Hardee 2006). Mean oral bioavailability of Mipopersen (ISIS 301012) in human clinical trials was only 6% (Hardee et al., 2006 Antisense Drug Technology, Ed. Crooke, 2nd Edition, Chapter 8). The clinical trial ISIS 301012 was terminated, and development has continued based on IV administration.
Oral delivery of oligonucleotides is particularly problematic due to the combined effects of extremes of pH within the digestive tract and the dilution effect, as well as inefficient absorption and transfer to the circulatory system. For example, the acidity of the stomach environment leads to depurination of purine bases and acid hydrolysis of the backbone of the oligonucleotide causes substantial degradation of the oligonucleotide.
Whilst one possible solution to the permeability problem may be to reduce the size of the therapeutic construct (Khatsenko 2000, Tsutsumi 2008), this creates the challenge of maintaining the required affinity, specificity and ultimately, potency of the antisense therapeutic. Shortening the length of oligonucleotides for oral delivery further raises the prospect that problems of oligonucleotide stability will be exascerbated as the effect of oligonucleotide degradation within the digestive tract will have proportionately a greater effect on shorter oligonucleotides than a longer one.
Khatsenko et al., Antisense & Nucleic Acid Drug Development 2000; 10:35-44 reports on the enhanced intestinal of PS-MOE oligonucleotides as compared to unmodified PS-ODN and that permeability increased linearly with decreasing length.
Tillman et al., J. Pharm. Sci. 2008; 97(1); 225-36 reports on the oral absorption of 2′MOE antisense oligonucleotides in healthy volunteers and that by pulsed delivery of the penetration enhancer sodium caprate, average plasma bioavailability of 9.5% was achieved. Tillman suggest that formulations can be devised that allow oral administration of oligonucleotides.
Herein, we disclose our surprising observation that Locked Nucleic Acid (LNA) oligonucleotides survive oral administration and are effectively absorbed in the mammalian digestive tract and provide a clear therapeutic benefit—i.e. they are not only bioavailable in sufficient quantities, but they survive in an intact and therapeutically active form, even without sophisticated formulation. Quite remarkably, the present inventors have found that LNA oligomers delivered simply with diet is effective in eliciting a therapeutically effective response.
LNA possess the necessary stability, potency and permeability to make oral dosing feasible, and is sufficiently robust to ensure the maintenance of the integrity of the oligonucleotide during oral administration to delivery to the site of therapeutic activity.
The present inventors have therefore identified LNA as a surprisingly superior chemistry for oral delivery, a chemistry which provides a robust therapeutic benefit to orally administered antisense compounds. Indeed, lower dosages of LNA oligomer can be administered whilst retaining pharmacological relevance, and surprisingly it was found that use of lower dosages or lower concentration of LNA oligomers, higher oral bioavailability could be obtained, especially when used in conjunction with a penetration enhancer.